Measuring devices

ABSTRACT

A PICKUP DEVICE IUS DISCLOSED WHICH MAY BE USED WITH A MAGNETIC FIELD IN A MEASURING SYSTEM. THE PICKUP DEVICE TAKES THE FORM OF A COIL WHICH, IN USE, IS CAPABLE OF CONFORMING TO A VARIETY OF SHAPES, AND AN IN CERTAIN FORMS IS CAPABLE OF FOLLOWING CHANGES IN SAID SHAPES WITHOUT RESISTIVE FORCE. THIS CONFORMABILITY OF THE COIL IS ACHIEVED BY A VARIETY OF COIL ARRANGEMENTS INCLUDING FORMS WHICH ALLOW THE COIL TO DEFORM WITHOUT RESISTANCE AND/OR BY MOUNTING THE COIL ON ELASTIC OR FLEXIBLE SUPPORTS, WHICH SUPPORTS CONFORM TO THE VARIOUS SHAPES. WHEN THE COIL IS POSITIONED IN A MAGNETIC FIELD IT GENERATES A SIGNAL WHICH IS A FUNCTION OF THE PARTICULAR SHAPE OR CHANGE IN SHAPE OF THE COIL.

Feb. 2, 1971 H. D. GOLDBERG ETAL 3,560,845

MEASURING DEVICES 8 Sheets-Sheet 1 Filed May.5, 1965 Indicator I8 I IRecord" Voltage Amplifiur Fig.2

Pow or Arnp'lifiur Oscillator Field pp y Fig.3

Fig.4

INVENTORS Horoki D. Goldberg By fgiltonl (iii-elbow ATT'YS H. D.GOLDBERG ETAL 3,560,845

Feb. 2, 1971' MEASURING DEVICES Filed May 5, 1965 8 Shoots-Sheet 2 Fig.6

INVENTORS Harold D. Goldblrg By Miil'." l. Goldberg Fig.9

ATT'YS.

Feb. 2, 1971 H. D. GOLDBERG ETAL 3,560,845

m rkwfii N NY WW Filed May 5, 1965 8 Sheets-Sheet 4 58,59- time is Fiuldsuppy Attenuator Voltuqc Ampmi" Record" INVENTORS Harold Goldberg MiltGoldbnrq Feb. 2, 1971 I H. D. GOLDBERG ET AL MEASURING DEVICES 8Sheets-Sheet '5 g-zi Fig.26 Fig.2?

Fig.28

INVENTORS Humid D. Goldberg Milfol. Goldberg da, $2 M ATT'YS l 3 n I Feb2, 1971 D, GOLDBERG ET AL 3,560,845

MEASURING DEVICES Filed May 5, 1 ,965 8 Sheets-Sheet 6 9 lndicu'or M3145I45 l4! 44 1-68 Fig.39 Fiq. 4o 1" INVENTORS Harold D. Goldberg BY Miltonl. Goldberg ATT'YS Feb.2, 1971 H. D. GQLDBERG ET 3,560,345

MEASURING DEVICES Filed May 5, 1965 8 Shees-$heet '1 Fig.43 -Fiq.44

Fig.4? Fig.48

JNVENTORS Harold D. Goldberg BY Milton Goldberg Feb. 2, 1971 v GOLDBERGETAL 3,560,845

MEASURING DEVICES Filed May 5, 1965 8 Shmets-Sheet 8 I'll Fiq.55

I77 |7| n4 |T2 7 I73 -l 2 '33 F 57 Fig.56

, INVENTORS Harold D. Goldberg By Milton l. Goldborq ATT'YS UnitedStates Patent Ofiice 3,560,845 Patented Feb. 2, 1971 3,560,845 MEASURINGDEVICES Harold D. Goldberg, King St., Port Chester, N.Y. 10573, andMilton I. Goldberg, Barrett Road, Katonah, N.Y. 10536Continuation-impart of application Ser. No. 4,766, Jan.

26, 1960, which is a continuation-in-part of applications Ser. No.374,782, Aug. 17, 1953, and Ser. No. 374,868, Aug. 18, 1953, which inturn are continuationsin-part of application Ser. No. 66,523, Dec. 21,1948. This application May 3, 1965, Ser. No. 456,885

Int. Cl. G01r 33/00 US. Cl. 324-34 74 Claims ABSTRACT OF THE DISCLOSUREA pickup device is disclosed which may be used With a magnetic field ina measuring system. The pickup device takes the for-m of a coil which,in use, is capable of con forming to a variety of shapes, and in certainforms is capable of following changes in said shapes without resistiveforce. This conformability of the coil is achieved by a variety of coilarrangements including forms which allow the coil to deform withoutresistance and/or by mounting the coil on elastic or flexible supports,which supports conform to the various shapes. When the coil ispositioned in a magnetic field it generates a signal which is a functionof the particular shape or change in shape of the coil.

This invention relates to instruments for measuring areas, volumes andrelated quantities, as well as other physical quantities such asdisplacements, forces, pres sures or the like, which can be transformedinto variations of areas, volumes or the like, this being acontinuation-in-part of our application Ser. No. 4,766, filed Jan. 26,1960, now abandoned, which is a continuation-inpart of our applicationsSer. No. 374,782 filed Aug. 17, 1953, now abandoned, and Ser. No.374,868 :filed Aug. 18, 1953, now Pat. No. 3,141,796, said applicationsin turn being a continuation-in-part of our application filed Dec. 21,1948, Ser. No. 66,523, which matured on Aug. 18, 1953, into Pat. No.2,649,573.

Among the important objectives of our invention is that of measuringcross-sectional areas of objects, both inanimate and animate. And inthis aspect of our invention it is an important object to avoid thecomplications and the errors, arising from various conditions oftemperature and other conditions, that frequently occur with the use ofcertain conventional measuring instruments. In the accomplishment ofthese objectives we employ, in accordance with our invention,electro-rnagnetic induction means embodying a conducting pick-11p coilencircling or embracing the member or region being measured, or aportion thereof, the coil and part which is being measured being placedwithin a uniform alternating magnetic fieldthe principle being that thevoltage induced in the coil by the field is directly proportional to thearea embraced by the coil. This method had been found to be accurate,capable of operation under conditions which would render otherconventional measuring apparatus impracticable or inaccurate, andadapted for a great variety of uses, as will more clearly hereinafter beset forth.

It is also within the contemplation of our invention to provide a devicecapable of measuring changes in crosssectional areas, such as may occurin portions of a body resulting from muscular contractions, etc., or inconnection with fluid flow in elastic tubes or in members of an animatebody.

During such changes in area as well as in like manner in changes inangle between the pickup and field there is induced within the pickupcoil an additional voltage which is displaced in phase by from that ofthe voltage induced when the area embraced by the coil is constant,these two voltages combining to produce a resultant voltage. While theformer voltage is proportional to the projected area of the coilmultiplied by 211- times the frequency of a sinusoidal alternatingmagnetic field, the latter is proportional to the rate of change of theprojected area of the coil. These voltages may be measured independentlyby circuits commonly known as phase-sensitive demodulators, the phase ofthe reference voltage determining the voltage detected. Suchdemodulators may measure the signal voltage over substantially theentire cycle or only over a selected portion of it.

When measuring changing areas, in order to faithfully follow them, thefrequency of the alternating magnetic field is normally selected as somemultiple of that of the highest frequency component of the changingarea. Also the changes in area are ordinarily only some fraction of thearea itself. Similarly, angular changes ordinarily result in relativelymoderate rates of change of projected area. Under these conditions theadditional induced voltage is small relative to the voltage due to thearea itself. Further, since the resultant of such voltages displaced inphase by 90 is equal to the square root of the sum of the squares of thevoltages, under the above conditions the effect of the additionalinduced voltage on the value of the resultant is negligible and isdisregarded in the following, except where specifically stated.

In connection with the last-mentioned aspect of our invention, it is afurther object to provide a device capable of measuring the pressure,velocity of pulsatile flow, the rate of flow, etc., and the behavior oftubes under conditions of stress, temperature, etc., in the field offluid dynamics.

Another object of our invention is to enable the ready and convenientmeasurement of volumes of solid or tubu lar bodies, an objective whichis accomplished by our invention by the integration of cross-sectionalareas with respect to the length of the section being measured.

And in further connection with the adaptability of our invention to themeasurement of fluid flow, it is a further objective to accomplish suchmeasurement by storing the effluent and measuring the rate of increaseof its volume, which equals the rate of flowan application thereof beingin the field of plethysmography, the measurement of the flow of blood inhuman or animal limbs or other parts of the anatomy by means of volumechange indications or recordings.

Yet another object of our invention is to enable the measurement ofrates of change of cross-sectional area and related quantities, anobjective which may be accomplished by our invention by using steadymagnetic fields for direct indications of rates of change of suchquantities. Alternative methods include selection of the aforementionedadditional voltage proportional to the rate of change of area inducedduring changes in area with a phase-sensitive demodulator, as well as byemploying suitable electronic circuits to differentiate the demodulatedvoltage proportional to the area, or under suitable conditions, theresultant voltage.

In addition to the use of steady magnetic fields and alternatingmagnetic fields of sinusoidal wave shape, other wave shapes, includingsquare, trapezoidal and various modifications of these wave shapes maybe employed to provide constant magnetic fields over portions of thecycle. These may be used in conjunction with demodulators which measurethe signal voltage only over such portions of the cycle or some fractionof such portions, giving an alternative method of measurement of rate ofchange of cross-sectional area, which yields certain advantages providedby a carrier frequency system of measurement.

It is also within the contemplation of our invention to effectuate themeasurement of position of an object by relating such position to theprojected area of a pick-up coil in an alternating magnetic field. Bythe use of steady and alternating fields, displacement, velocity, force,and related quantities may be measured, as well as various functions ofthese quantities, by methods including the use of suitable pick-upstructures and nonuniform fields-an application of this aspect of ourinvention being in the field of general strain gauging. Among theadvantages of this method are that very little force is required todeflect the pick-up, that a very wide range of function relating outputvoltage and position and related quantity is possible, that theassociated circuits are simple and may be made free from drift, and thatdevices incorporating the method are easily produced.

Another object of our invention is the provision of a device capable ofgeneral measurement of irregular areas, such as those defined byboundary lines, for example, mathematical and other curves, maps,charts, etc. In this aspect of our invention the conductor defining thearea, instead of being the pick-up coil above mentioned, is a line ofconductive material, which may be elastomeric, or a length ofconductor-the voltage induced in this conductor when placed in a uniformalternating magnetic field being directly proportional to the definedarea. For performing mathematical operations on curves, non-uniformmagnetic fields, as well as curves outlined on deformable sheets, may beemployed. This aspect of our invention has application in the fields ofmathematics, computation, cartography, and others, as well as in themeasurement of elastic members, including the study of stresses.

Yet a further object of our invention is to provide a pick-up coilparticularly adapted for adjusting embracing engagement with orencirclement of the surface of a member to be measured, and soconstructed and arranged whereby the voltage operatively induced thereinwill be affected only by the change in the embraced area, and willremain substantially unaffected by other changes in dimensions,proportions and shape of the coil during its expansion.

Still a further object of our invention is to provide a pick-up coilparticularly adapted for measurement of any quantity which may cause achange in the number of lines of force of a magnetic field enclosed bysaid pick-up.

Other objects, features and advantages will appear from the drawings anddescription hereinafter given.

Referring to the drawings,

FIG. 1 is a schematic drawing of one form of our invention, showing thefield and pick-up coils and their electrical connections.

FIG. 2 is a perspective view of a member being measured, with a pick-upcoil operativel placed thereover, the drawing further schematicallyillustrating the field coils and electrical connections, as Well as themagnetic field.

FIG. 3 is a fragmentary prespective view of a member being measured witha pick-up coil placed thereover, the

coil being substantially like that illustrated in FIG. 2, and beingshown in its condition before the expansion of the member.

FIG. 4 is a view like FIG. 3, but showing the parts in their expandedcondition.

FIG. 5 shows a fragmentary perspective view of a multiple pick-uparrangement over a member of nonuniform cross-section.

FIG. 6 illustrates a fragmentary perspective view of a helical form ofpick-up member operatively disposed upon a member being measured.

FIG. 7 shows a fragementary perspective view of a multiple pick-uparrangement with a plurality of aligned coils disposed in substantiallyparallel planes and connected in series.

FIG. 8 shows a fragementary perspective view of another multiple pick-uparrangement with a plurality of aligned coils in substantially parallelplanes, and connected in parallel.

FIG. 9 is a fragmentary perspective view of a member being measured witha pick-up coil disposed on a tape helically wound around the member.

FIG. 10 is a semi-schematic perspective view of a tape substantiallylike that shown in FIG. 9, illustrating the pick-up conductor disposedon an outer surface of the tape and connected to conductor leads whichare joined to form a twisted cable.

FIG. 11 is a longitudinal cross-section view of another form of pick-upmember that could be wound around the member being measured,substantially in the manner illustrated in FIG. 9, the conductor elementbeing a conductive liquid.

FIG. 11a is a cross-section view of FIG. 11 taken substantially alongthe line 11a11a.

FIG. 12 is a semi-schematic perspective view of a section of an elastictape substantially like that shown in FIG. 10, but with the pick-upconductor moulded into the body of the tape.

FIG. 13 is a front view of the structure of FIG. 12.

FIG. 14 is a central axial sectional view of an inflatable pick-updevice for use in our invention, the device being shown in operativecondition with respect to a member being measured.

FIG. 15 is an end view of the structure of FIG. 14.

FIG. 16 is an axial sectional view of the structure of FIG. 14, butshowing the inflated portion in its expanded or operable condition, incontact with the outer surface of the member being measured.

FIG. 17 is an end view of the structure of FIG. 16.

FIG. 18 is a fragmentary perspective view of a member being measured,with a soft sponge-like sleeve disposed thereabout and having a pick-upcoil on the inner surface thereof.

FIG. 19 is a vertical sectional view of the device of FIG. 18.

FIG. 20 is a perspective view of the device of FIG. 19, showing anadditional auxiliary coil of fixed configuration as a source ofcompensating voltage.

FIG. 21 is a schematic drawing showing the field and pick-up andauxiliary coils of FIG. 20, the circuit being substantially like thatshown in FIG. 1.

FIG. 22 is a fragmentary perspective view of a member being measuredwith a tubular knitted pick-up member placed thereover.

FIG. 23 is a diagrammatic representation of the knitted structure of thetubular member of FIG. 22, the drawing showing a fiat portion of saidknitted fabric.

FIG. 24 is a view substantially like FIG. 23, but showing a modifiedform thereof in which there are alternate conductor and non-conductorstrand elements.

FIG. 25 is a schematic representation of a sheet of woven fabric adaptedto be formed into a tubular pick-up member.

FIG. 26 is a fragmentary diagrammatic perspective view of a member beingmeasured, with a special form of pickup member adapted for measuring afragmentary circumferential portion of the member.

FIG. 27 is a semi-diagrammatic partially sectional view of the structureof FIG. 26, showing the pick-up member operatively applied to the memberbeing measured.

FIG. 28 is a semi-diagrammatic view of the pick-up member of FIG. 26,showing the flexible pick-up coil in an extended position for obtainingthe area between said flexible pick-up coil and the rigid arcuateconductor.

FIG. 29 is a semi-diagrammatic View showing the application of thepick-up member of FIG. 26 to a member being measured, the shaded areasrespectively representing the indicated area and the area to bemeasured.

FIG. 30 is a semi-diagrammatic perspective view of the general type ofpick-up device of FIG. 26 adapted for making substantially completecircumferential measurements of members.

FIG. 31 is a vertical sectional view of an inflatable pickup device likethat of FIG. 14, adapted for making internal measurements of members.

FIG. 32 is a sectional view of the structure of FIG. 31, but showing thedevice inflated, in its expanded or operable condition, in contact withthe inner surface of the member being measured.

FIG. 33 is a fragmentary schematic drawing showing the field coilsreplaced by pole pieces of a permanent magnet.

FIG. 34 is a perspective semi-diagrammatic view of an electromagnet andpick-up coil and their electrical connections for measuringdisplacement, velocity, and related quantities.

FIGS. 35 through 46 are schematic drawings showing various forms ofpick-ups which may be used with a field structure such as that of FIG.34, for measuring displacement, velocity, and related quantities.

FIG. 47 is a schematic drawing showing a pickup adapted for attachmentto a surface undergoing changes in dimensions.

FIG. 48 shows an end view of the structure of FIG. 47.

FIG. 49 is a fragmentary semi-diagrammatic view of a pick-up and a pairof shaped pole pieces which may replace the pole pieces of FIG. 34.

FIG. 50 is a perspective semi-diagrammatic view of an electromagneticfield structure and pick-up, including electrical connections, as usedin a flowmeter.

FIG. 51 is a semi-diagrammatic front view and FIG. 52 is a centersectional view of a form of pressure-measuring device.

FIG. 53 is a semi-diagrammatic front view and FIG. 54 is a centersectional view of another form of pressuremeasuring device.

FIG. 55 is a schematic drawing showing a mathematical curve, of whichthe area outlined is the quantity to be measured.

FIG. 56 is a semi-diagrammatic perspective view of a mathematical curvetogether with a structure designed to simplify the attachment ofconnecting leads thereto when used in the measurement of areas outlinedby curves.

FIG. 57 is an enlarged semi-diagrammatic perspective drawing of the leadattachment structure of FIG. 56.

As aforesaid, the essecne of our invention resides in the use ofelectro-magnetic induction to measure crosssectional areas and areachanges and rates of change, and other quantities which can be made tocorrespond to such areas and area changes. In one form of practicing ourinvention, as will more in detail hereinafter be described, analternating magnetic field is suitably produced, as by anoscillator-amplifier field coil setup; and in this field an expansiblepick-up coil is placed, encircling the member or area being measured,the axis of the member being positioned parallel to the magnetic field.The pick-up coil (hereinafter called the pick-up) is so constructed thatan increase and decrease in its cross-sectional area can be producedwithout the employment of ap preciable force. The arrangement is suchthat the voltage induced in the pick-up may be amplified by suitableelectronic equipment, where desired, and observed by means of anoscilloscope or other indicating or recording means.

In FIG. 1 of the drawings the field coils 10 and 11 are illustrated asbeing of substantially equal diameters and as flanking the pick-up 12,the latter being shown as smaller than the field coils, disposed midwaytherebetween, and adapted for embracing and contacting engagement with amember to be measured. The pick-up 12 is preferably so constructed thatchanges in its crosssectional area can be produced without theemployment of appreciable force. The field coils may be Helmholtz coils,solenoids or other magnetic-field-producing devices, including thoseusing cores of magnetizable materials, and are operatively energized byany means known in the art, such as by a suitable field supply 13, or bythe com bination of an oscillator 14 and power amplifier 15 suitablyelectrically connected to each of the coils as schematically illustratedin FIG. 2. The energization of the field coils produces an alternatingmagnetic field, the central portion of which extends substantiallyparallel to the axes of the field coils and pickup, and is interceptedby the pick-up. Since the member being measured, such as the cylindricalmember 16 of FIG. 2, extends axially through the pickup, said member isparallel to the magnetic field, and any change in the diameter of themember will be transverse to the direction of said field. And as thepick-up 12 is flexible and adjusting, according to a construction to behereinafter described, any increase in the member being measured willcause a corresponding increase in the diameter and area of the pick-upcoil, thereby enclosing more of the lines of force of the field. Thearrangement is obviously such that a voltage will be induced in thepickup 12 which is proportional to the number of lines of force of thefield enclosed by the pickup, and this voltage may be observed byequipment connected to the pickup such as indicator 14 of FIG. 1, whichmay be a sensitive voltmeter, or a voltage amplifier 17 and recorder 18electrically connected to the pick-up, as shown in FIG. 2.. With auniform field the induced voltage will be proportional to thecrosssectional area of the member embraced by the pickup.

Any change in the cross-sectional area of the member being measured willcause a corresponding change in the cross-sectional area of the pick-upcoil, thereby changing the number of lines of force of the fieldenclosed by the pick-up, and hence correspondingly changing the voltageinduced in the pick-up. Thus crosssectional area changes as well ascross-sectional areas may be measured. Also, should it be desired tomeasure the volume of a member such as 16, whether it be an animate orinanimate object, cross-sectional areas may be integrated with respectto the length of the member, so that volumes and volume changes may alsobe measured.

This is done by taking measurements from other pickups distributed alongthe length of the member being measured, and summing the products ofeach measurement times the separation of the respective pick-up from itsneighbor. Instead of having a plurality of pick-ups, a single pick-upmay be moved to successive positions along the member, the summationthen being of the products of each measurement times the correspondingdisplacement. The greater the number of measurements in each case, thegreater will be the accuracy of volume measurement. Thus, by the use ofour instrument or system above described, volume changes may be obtainedby integrating changes in cross-sectional areas. The readings measurechanges in the voltage output, and these are readily translatable intovolume changes.

By using steady magnetic fields or by other methods herein abovedescribed, readings may be obtained which are proportional to the ratesof change of area and volume. When applied to a limb, the volume changesper second produced by the usual procedures of plethysmography areobtained by integrating the changes in crosssectional area per second,the results being related and expressed in volume changes per second perunit of initial volume of tissue.

The specific pick-up coal 12a illustrated in FIGS. 2 to 4 consists of asingle turn of fine-gauge conducting wire, although it is without ourcontemplation to employ, where necessary, a pick-up arrangement having aplurality of adjacent coils or a coil with a plurality of turns. For thepurpose of this specification, however, the term pick-up coil will bebroadly used to cover any of these constructions. The wire of the coilis of soft temper, the wire being of wavy configuration substantiallythroughout its entire extentthe bends which form the wavy configurationextending generally in the direction of the axis of the pick-up coil,and lying in a surface which is substantially parallel to the surface ofmember 16 embraced by the coil 12a, and forming a plurality of angles 19between each wave formation. In other words,

the wavy zig-zag formations extend in a direction substantially at rightangles to the plane of the pick-up coil. Hence, if the pick-up coil 12ais in embracing engagement with the peripheral surface of member 16, itwill change its cross-section therewith in the event said member 16 iscaused to change its cross-section. The waves or undulations in thepick-up coil 12a obviously permit such expansion therefor; and duringthis expansion, the only material change that takes place in the coil isin the angles 19. This change or deformation of the wavy portions ofcoil 12a does not, as a practical matter, by itself affect the voltageinduced therein, since this represents changes substantially in adirection parallel to the magnetic field, represented by the lines 20.This is true even 'where the member being measured is not of uniformcross-section throughout its length, the compensating or opposingchanges in the wavy portions of the pick-up coil obviously producing incorrect average values. Of course, the concomitant change in areasurrounded by the coil will correspondingly vary the voltage as isdesired in making a measurement of area change.

Thus, the use of a pick-up coil of the above-described construction isparticularly adapted for use with our apparatus, since it changes itsarea together with the changes in area of the embraced member beingmeasured and does not, during the process of expansion or contraction,introduce extraneous factors which may have an effect upon the inducedvoltage. The thinness and softness of the wire permit the coil to expandreadily with the increase in cross-section of the embraced member, sincevery little force is necessary to overcome the resistance the wireaffords to such an expansion. It should be observed that if the wirewere not readily responsive to the expanding action of the member beingmeasured and would not easily expand therewith, it would exert a bindingeffort around the embraced area and thereby hinder its expansionanaction which would be particularly objectionable in the case of themeasurement of soft tubes or living tissue. Alternate constructionsinclude forming the conductor into other yieldable configurations suchas helical, i.e., in the shapes of coil springs, as well as the use ofother forms such as various sliding and jointed structures.

While certain of these alternate constructions, such as the helical,introduce an error into the measurement, since portions of the conductorare spaced from the surface of the member, such pick-ups may beapplicable to measurements of limited accuracy where ease of fabricationand application may be important. The use of a coil with small andflattened diameter minimizes this error. Also mathematical correctionsderived from the dimensions of such pickups may be applied. Thefabrication and application of such pickups may be facilitated bywinding the conductor about a core of suitable expansible material orencasing it within a tube of such material, with or without a core. Alsoa removable, relatively non-extendible cord of shorter length than theextended conductor may be included with such a pickup as a temporarycarrier to facilitate its fabrication and handling preparatory to use.

It will be noted that, as shown in the drawing, the lead conductorsextending from the pick-up coil are twisted together. This is termed anon-inductive susceptive relation, and is useful here in avoidingspurious induced voltages due to the lead conductors rather than to thepickup coil.

The pick-up coil 12a may be applied to the member being measured by anyof several different methods. Under certain conditions it would besatisfactory to apply the coil 12a directly upon the member 16 withoutany holding means other than the resiliency of the wavy wire itself, asis indicated in FIGS. 3 and 4 which show the pick-up coil and embracedmember in their normal and expanded condition, respectively. However,the wire is preferably essentially non-resilient, and the coil may becemented to the surface with a suitable elastic medium, or may beyieldably held against the surface by an inflated cuff, or by an elasticcuif.

Where a single cross-sectional area is to be measured, a single pick-upcoil 12a is employed, as shown in FIGS. 3 and 4. However, should it bedesired to obtain volume measurements, a plurality of pick-up coils 12bare arranged in spaced relation on the member to be measured. Thus, inFIG. 5, a non-uniform member 16b is shown operatively embraced by fourseparate pick-up coils 12b, the separate area results for each pick-upbeing integrated along the length of the member to obtain volumeresults.

Instead of separate pick-ups 12b, a helical pick-up 120 (FIG. 6) may beoperatively placed over the member 16c-the voltage produced by thisarrangement being proportional to the volume of the member along thelength being measured.

FIG. 7 represents a pick-up device substantially lik that of FIG. 5,there being four separate pick-up coils 122 in substantially parallelplanes, but arranged in series with respect to each other and the leads36 and 37, to provide either an average area measurement or a volumemeasurement as in FIG. 6. It will be noted that the winding of each coilreturns substantially to the region of its start, the connectingconductor between coils extending at right angles to the planes of thecoils. Thus, lead 36 is connected to the extreme left-hand coil 12a atpoint 38, to emerge at point 39 adjacent to point 38. The emergedportion 36a of the conductor is connected at point 38a of the next coil,the connection continuing in series with the coils to point 40 of theextreme right-hand coil, thereafter to return by conductor 37a to thetwisted cable shown at the left. It will be noted that the conductors36a and 37a are adjacent to each other and cross each othersymmetrically, and are substantially at right angles to the planes ofthe coils. The arrangement is such as to minimize extraneous pick-up. Inthis respect the connected form of pick-up illustrated in FIG. 7 issuperior to the helical type above referred to, for in the latter thereis some possibility that stray fields which make an angle with the axisof the helix will induce some extraneous voltage. However, with theconnected form of construction of FIG. 7, there is ideally no voltageinduced by stray fields at right angles to the axis of the coils, sincethe projected area of the coils is substantially zero, and since theconnections between the coils and the lead wires are, as illustrated,close together and cross each other symmetrically.

FIG. 8 shows an arrangement similar to that of FIG. 7, but one in whichthe coils 12 are connected in parallel by the closely spaced parallelconductors 41a and 42a extending from the leads 41 and 42 of the twistedcable shown to the left. In this arrangement, when equal weighting is tobe given the signal induced in each conductor, they should be of equalresistance. This parallel connection is of convenience in theconstruction of a pickup in strip form, to be wrapped around a member inthe manner above-described, since in such a case it is not necessarythat the coils form successive circuits around the member beingmeasured.

It maybe stated that where reference is made to the use of a pick-upconductor, it is to be understood that this conductor may, in certainforms of this invention, be made of a number of strands, which may beinsulated. And in order to accurately measure the cross-sectional areaof a member, it is desirable that the pick-up be held in such relationto the member that it faithfully follows the contour of the memberwithout distortion, and without hindering the expansion of the member orfailing to follow its operative contraction. In order to accomplishthese objectives, there are various forms and manners of fabricatingpick'up devices, in accordance with our invention. For example, as willmore clearly hereinafter appear, pick-ups may be attached to flexiblematerial in the form of a length of tape or a cuff or tubethe flexiblepick-up conductor being attached to the supporting material by sewing,cementing or other known means. A conductor to serve as a pick-up may beattached to woven or knitted material, in zig-zag configuration or othersuitable arrangement; and the entire pick-up structure may itselfconstitute the whole or a part of a suitably woven or knitted materialhaving strands of conductors suitably connected to the measuringcircuit, all in a manner to be hereinafter referred to.

FIG. 9 illustrates one form of attaching a pick-up conductor to asupport which itself is adapted to be wrapped around a member beingmeasured. The pick-up conductor 12g, extending from leads 43 and 44, isplaced on the underside of the helically wound expandable tape 45disposed about the member being measured. This provides one practicalmethod of employing the helical construction illustrated in FIG. 6.

FIG. 10 illustrates one form of expandable tape carrying a pick-upconductor. In this form the pickup conductor 1211 is a wire applied tothe tape by any convenient method known to those skilled in the art. Forexample, the conductor 12h may be applied in zig-zag form byconventional sewing machine methods which are adapted to form suchconfigurations of sewn threads; or the said conductor 1212 may beadhesively secured upon the outer surface of said tape 46.

FIGS. 11 and 11a show a flexible pick-up construction comprising aconductive liquid (which may be viscous) encased in a properly shapedextendable nonconductive tube. In the particular form illustrated, theflexible nonconductive extensible tube 47 contains therein theconductive liquid 48, the plugs 49 at the end of the tube 47 sealing theconductor within the tube. The plugs 49, which are of conductingmaterial, are electrically connected to the leads 50 and 51, these beingadapted to be connected to the measuring circuit in the mannerabove-described. This form of pick-up, with the tubing 47 of flat thinwalled configuration, is particularly adaptable to be wound around amember being measured.

FIGS. 12 and 13 represent still another form of flexible tape type ofpick-up member. In this form, the conductor 12i is encased or mouldedwithin the body of expansible tape member 52, this being of rubber orother suitable elastomeric non-conducting material. The pick-upconductor 12i is connected to the leads 53 and 54, and these are adaptedfor connection to a circuit in the manner above-described. It isimportant to note that this type of pick-up is to be distinguished fromthe other types hereinabove described in that the pickup conductor 112iis not adapted for contacting engagement with the member being measured.Only the undersurface 56 of the tape is to be placed in engagement aboutthe outer periphery of the member being measured. Alternatively, anelastomeric conducting material may be encased or molded within the bodyof the tape, or may be used directly in the form of a tape.

FIGS. 14 to 17 show a pick-up device adapted for convenient andeffective use with our systemparticularly desirable because it insures ayieldable and complete contact with the outer surface of the memberbeing measured. This form of our invention employs an air pressure cuff30 comprising, in its illustrated form, a tubular member 31 and attachedthereto, along the peripheral position thereof, the inner elastic wall32 forming an annular air chamber 33 between elastic wall 32 and member31. The air inlet tube 34 is attached to member 31 and communicates withthe air chamber 33. The medial portion of the annular wall 32 hassuitably attached thereto the pick-up coil 12d adapted for contactingengagement with a member to be measured, such as 35.

When operatively employing said device, the chamber 33 receives airunder pressure through tube 34, causing the wall 32 to expand inwardlyuntil the pick-up coil 12a is brought into engagement with the outersurface of member 35. Thereafter, as the member 35 is caused to expand,the pick-up coil 12d will also expand against the resilient air cushionsurrounding it in the form of the inflated Wall portion 32. Tofacilitate bringing the pick-up into and maintaining it in conformanceWith the member 35 a layer of spongelike material may be includedbetween wall 32 and pick-up 12d.

The last-described form of pickup is particularly adaptable for use inmeasuring cross-sectional areas of both animate and inanimate objects,as are other form of picloup described herein.

The form of pick-up illustrated in FIGS. 14 to 17 is so constructed thata substantially uniform force is exerted against the pick-up atsubstantially right angles thereto. Another method of providing asimilar force to the pickup is illustrated in FIGS. 18 and 19 in whichthe member 57 being measured is surrounded by sponge-like resilientpick-up cuff '55 which contains, along the inner surface thereof, thewavy pick-up conductor 12 this being electrically connected to leads 58and 59. The proportions of this ressilient cuff are such that it willyieldably hold the pick-up in light pressing engagement with the memberbeing measured. In addition, the sponge-like material may be compressedagainst the pick-up and member by the use of an additional outer layerof suitable material. It may also be more convenient in certain cases toapply the sponge-like material in the form of a strip, tape, or otherform, wrapped around the pick-up and member and fastened into a cuffwith or without an external band.

In connection with applications involving changes of area the voltagecorresponding to an initial area may be balanced out, to provide adirect reading of the change in area. An auxiliary coil may be employedas a source of balancing voltage and mounted in the same or acorresponding magnetic field, of adjustable or fixed area; in the lattercase, the induced voltage being externally controlled. This procedure ofbalancing out an initial quantity is commonly called zero-suppression.

In general, the voltages induced. in a pick-up are, as above set forth,determined by its cross sectional area, among other factors. If thepick-up should change orientation, its projected area (i.e., the areaprojected on a plane perpendicular to the direction of the field) wouldbe correspondingly changed-and its induced voltage will be affected,even though the cross'sectional area of the member being measured hasnot changed. Such efiect may be compensated for by a number ofprocedures.

One normally applicable employs a non-expansible auxiliary coil 60, offixed dimensions (see FIG. 20) attached to the member 57 being measuredso that it follows the latters orientation. This auxiliary coil, whichmay surround the member or not, and may be considerably smaller than thepick-up coil, may be positioned so that its projected area remainsproportional to that of the pick-up coil independent of angle ofprojection. This may be accomplished by orienting the member withrespect to the direction of the field so that maximum voltll age isinduced in the pick-up, and then orienting this auxiliary coil for acorresponding induced voltage. An alternative is orienting in twodirections, preferably mutually perpendicular for zero induced voltages.

Alternative to the use of a single coil which requires orientation, aset of three coils which may be mutually perpendicular may be employed.The voltages induced in the coils, suitably independently controlled,may be combined to yield an output voltage which is also proportional tothat of the pick-up coil, independent of angle of projection. In themutually perpendicular case effective orientation may be accomplished byadjusting the output of each of the set of three coils to a fixed ratioto that of the pick-up while the field direction is perpendicular to theplane of that coil, at which orientation its induced voltage is amaximum, and the induced voltage of the other two coils of the set iszero. In the following, coil 60 will be used to refer to either a singlecoil or such a set of three coils.

The voltage obtained from coil 60 may be used to control the sensitivityof the indicator as by controlling the gain of an amplifier driving orincluded in the indicator, in a conventional manner and so compensatefor the effect due to change in orientation, which changes the outputfrom the pick-up coil.

Of course, compensation cannot be provided over an unlimited range oforientations. For example, it is obviously ineffective when an area isat such orientation that its pick-ups output approaches zero.

Alternatively voltage obtained from coil 60 may be used as a referenceagainst which the voltage of pick-up 12 is compared. In this case alsothe effect due to change in orientation is compensated for.

The voltage obtained from this coil may also be used as a source ofzero-suppression voltage, this voltage varying proportionately with thepick-up voltage. The 90 phase displaced component of this voltage,induced While the coils orientation changes is an additionalcompensating factor, and is also available for other purposes. Thisprocedure is also effective in reducing spurious voltages induced bystray fields, or variations in the applied field.

Alternative means for rendering the output of a pickup independent ofits orientation within a magnetic field include the use of magneticfields capable of variation in orientation, as well as the use of aplurality of magnetic fields.

Illustrative of procedures employing fields of adjustable orientation isthe use of fields whose orientations (which may be mechanically orelectrically adjustable) are related to those of pick-ups through manualor automatic control. Tracking methods include the maintenance ofmaximum pick-up output, or constant output from auxiliary rigidpick-ups. Alternatively zero induction may be maintained from auxiliaryfields (which may differ in characteristics) angularly displaced from,and controlling the main field.

Another general procedure for rendering output independent oforientation is the use of fields which scan required orientations.

Various scanning procedures may be employed including the use ofrotating fields, whose axes of rotation may also rotate or otherwiseencompass required orientations.

As hereinabove mentioned, yet another procedure for rendering outputindependent of orientation is the use of a plurality of magnetic fields.This may preferably consist of a set of 3 mutually perpendicularalternating fields. They may be of the same frequency appliedsequentially or of different frequency or other characteristic appliedsimultaneously.

In the case of fields of the same frequency, their strengths areordinarily adjusted to equality. Since the output voltage induced in thepick-up by each of the fields is proportional to the projected area ofthe pick-up on a plane perpendicular to the direction of the field, theeffective area of the pick-up is proportional to the square root of thesum of the squares of the separate induced voltages. Electronic circuitsmay be employed for combining the output voltages in this manner.

In the case of fields of diiferent frequency, which may be appliedsimultaneously the same general procedure would be followed, except thatsince the voltage induced in the pick-up by a field is dependent uponthe frequency of that field either the field strength, or the utilizedfraction of the induced voltage at each frequency may be selected oradjusted so that the output voltage per unit area at each frequency isthe same. Further, since the output voltage induced in the pick-up byeach of the fields, when adjusted by such procedures, is likewiseproportional to the projected area of the pick-up on a planeperpendicular to the direction of the field, the output voltages at thedifferent frequencies may be separated, demodulated and the square rootof the sum of the squares determined by electronic circuits asaforesaid, which separation and demodulation may be combined in a singleelectronic circuit.

If required the angle the pick-up effectively makes with the directionof the magnetic fields may also be indicated by suitable electroniccircuits.

One manner in which the pick-up coil 12 and the auxiliary coil 60, whenused for balancing, are connected in the circuit is illustrated in FIG.21. It will be seen that the leads 58 and 59 of the pick-up coil areconnected to the amplifier 64, in series with the balancing voltagederived from the auxiliary coil 60, through the leads 61 and 62, theamplitude of this balancing voltage being adjusted by means such asattenuator 63 or other conventional means.

As above stated, pick-up coils for our invention may be in the form oftubes or sleeves, the conductor member comprising a plurality of strandsarranged in interengaging formation, either knitted or woven. Such atubular or sleeve-like construction is extremely flexible, and canreadily conform itself to the proportions and variations of the memberbeing measured. The individual conductor strands need not themselves bestretchable or elastic, although the fabric into which they are woven orknitted is itself stretchable, either in one or two directions,depending upon the structure of the fabric. FIG. 22 shows the member 65(being measured) enveloped by pick-up conductor 12k made entirely ofknitted construction, the leads 67 and 68 being connected to oppositelateral courses, as more clearly appears in FIG. 23, which shows aknitted jersey construction.

In the yieldable knitted construction of FIG. 23, there are a pluralityof horizontal courses and intersecting wales, as is well known to thoseskilled in the art, the opposite or end courses being represented by theupper course 69 and the lower course 70, respectively. It will be seenthat lead 67 connects with strand 67a in course 70, and that lead 68connects with strand 68a which extends directly into course 69. In theillustrated diagrammatic illustration of the development of knittedfabric, the dot-dash lines show how one course is connected with thenext adjacent course, in known manner.

The arrangement is hence such that when the fabric of FIG. 23 is formedinto tubular configuration, and placed about the member being measured,it will conform to the configuration of the member. Any variations willcause an expansion or retraction of the tube; and since said tubeconstitutes a pick-up conductor in the magnetic field, readings can beobtained, in the manner aforesaid. It will also be observed that thedirection of strand 68a is at right angles to the direction of theknitted courses, the terminal portions of strands 67a and 68a beingpreferably in adjacent relation, to engage with each other to form theconventional twisted cable illustrated.

If it is desired, the strands constituting the fabric may be made ofspring-like material, one such material being beryllium copper. Tofurther assure contact with the 13 member being measured, theconstituent strands of the fabric may either be cemented down to themember being measured, or held thereagainst by an external sleeve.

In certain instances of these constructions, it is advisable to employcourses of a fibre like nylon in the tubular fabric, in addition tocourses of the conductive strands, principally to effect improvements inthe mechanical properties of the enveloping fabric. FIG. 24 shows onesuch construction. The entire pick-up 12-1 is a knitted fabric,substantially like that of FIG. 23, but showing courses 75, 76 and 77made of non-conducting fibre, like nylon, whereas courses 78, 79, 80 and81 are made of conducting material, as fine copper wire. Strand 82extends downwardly from the upper course 81 and joins strand 83 fromlower course 78, to form the twisted cable from which emerge the twoleads 84 and 85. Here, as in the previous illustration, the dot-dashlines show the connections between adjacent rows to complete a tubularconstruction, in known manner. This construction is particularly usefulwhere a soft conductor, like copper, is employed, the nylon impartingelasticity as Well as general strength to the entire fabric, without inany other way substantially affecting the operation of the pick-upmember.

FIG. 25 is illustrative of a woven pick-up member 12m. Here there areconventional wrap and woof strands 86 and -87 interwoven, one of thestrands being a conductor, which may be of elastomeric material. Theschematic showing is not intended to limit the strands to straightlengths, since they may, within the contemplation of this invention, begenerally loosely interwoven, and of wavy configuration, and cemented orotherwise secured together, if deemed necessary. From the uppermostcourse 88 the strand 90 extends downwardly to join strand 91 from thelowermost course 89, adjacent terminals of these being twisted to formthe cable terminating in the leads 92 and 93. When this woven form ofpick-up conductor is employed, it is formed into a tube similar to thatof the knitted form above described, for placement on a member and aspart of a suitable circuit as above indicated.

Our invention is also adapted to obtain measurements of partialcircumferential regions of a member, or of different sections of amember being tested. This is par ticularly useful for certain forms ofuniformity tests, where area measurements must be taken in differentplanes, or in different sections of one plane of a member, or where themember being measured is not adapted to be encircled by the pick-up. Thepick-up construction shown in FIGS. 26 to 29 is adapted for such use.

FIG. 26, shows, in perspective, and FIG. 27 in part section,diagrammatic representations of a substantially cylindrical member 95operatively engaged by a pick-up device, said pick-up device comprisingthe flexible expandable pick-up conductor 12nand the relatively rigidarched conductor 96. One end of said pick-up conductor 12n is connectedto the corresponding end of said rigid conductor 96, their opposite endsbeing connected at juncture 100, to a twisted cable formed of leads 97and 98. An initial reading, with pick-up conductor 12n stretched acrossthe opposite terminals of rigid conductor 96 (FIG. 28) is taken bymeasuring apparatus to which leads 97 and 98 are operatively connected,in the manner above described. By referring to FIGS. 27 and 29, it willbe seen that conductor 12n is placed over a peripheral portion ofcylindrical member 95. A second reading may now be taken by saidapparatus. If I indicates the area pick-up is stretched across theopposite terminals of the rigid conductor when the rigid conductor (FIG.28), and area II represents the area indicated by the measuringapparatus ,(FIG. 29), the desired area III is the difference betweenareas I and II (FIG. 29). For convenience in making such measurements,the area indicated when stretching said pick-up across oppositeterminals of said rigid conductor may be balanced to a zero reading,where-upon a desired area is represented directly by the reading whensaid pickup is applied to a member. Correspondingly, changes in crosssectional area are represented by differences in readings before andafter the changes.

It is apparent that the structure and inventive principle of the pick-upmember shown in FIGS. 26 to 29 can be employed not only for thefragmentary cylindrical surface illustrated, but also for irregularsurfaces, as well as concave, and for measurements within a hollowtubular portion where pick-up conductor 12n is placed in operativeengagement with an inner surface, and also for substantially completecircumferential measurements. In the latter case, the aforementionedrelatively rigid conductor forms a substantially closed loop, as shownin FIG. 30. One end of pick-up conductor is connected to thecorresponding end of said rigid conductor 96, their opposite ends beingconnected to a twisted cable formed of leads 97 and 98. The structurehere illustrated is especially convenient in certain applications, forexample where it is desirable to clip an assembled pick-up and cableradially over a member. For such applications, conductor 96 is soconstructed that its ends may be separated to permit this to be readilyaccomplished, for example, by making it of a conductor which, whilerelatively rigid, is also elastic so that it returns to its originalconfiguration after having been expanded, or by providing it with ajoint so that it may likewise be returned to an original configuration.The cross sectional area of the member may be determined in the generalmanner described with reference to FIGS. 27 to 29. However, forconvenience, the pick-up may be applied to a known cross-sectional areato permit ready determination of the area enclosed by rigid conductor96. For volume measurements, multi-turn pick-ups of this general typemay be employed, for example, by the use of a plurality of adjacentturns.

As aforesaid, pick-up conductors may be placed in operative engagementwith inner surfaces. For measurements of internal cross sectional areasand volumes, they may be held in such engagement by various methods,including cementing, and the use of means for maintaining pressingengagement, in general, as above described. For example, FIGS. 31 and 32show, in cross section, a diagrammatic representation of a hollow member100, with a form of inflatable pick-up device adapted for convenient usefor internal measurements. Yieldable expansible pick-up conductor 121)is shown suitably attached to the wall 101 of elastomeric tubularstructure 102, which is provided with inlet 103.

When operatively employing said device, fluid, which may be air, underpressure, is admitted through inlet 103, causing wall 101 to expandoutwardly, until pick-up conductor 12p is brought into operativeengagement with the inner surface of member 100, as shown in FIG. 32. Anadditional use of a fluid pressure cuff is the measurement of the crosssectional area of a member, and changes in it, under conditions ofvarying pressure against it, this being accomplished by simply varyingthe pressure in chamber 33.

The principle and structures of the pick-up devices illustrated in FIGS.14 through 17, and 31 and 32, in addition to their use in bringing apick-up device into operative engagement with a member for area andrelated measurements, may be employed independently as forms of pressuremeasuring device. In such case, suitable elastic tubular or otherstructures may be employed to permit the establishment of desiredrelations between the induced voltage and the pressure being measured.

In employing our system for plethysmographic purposes, as aboveindicated, the conventional venous occlusion method is used, permittingmeasurements of the total blood flow. This can be accomplished in themanner described in the previously filed application, Ser. No. 66,523now Pat. No. 2,649,573. The same method renders our invention adaptablefor the general measurement of fluid flow Where elastic non-conductingtubes can be employed as a conduit for a fluid, by storing the efiiuentand measuring, by the method above-described, the rate of increase ofvolume, which equals the rate of flow.

The foregoing forms of the invention have been described With respect tothe use of an alternating magnetic field. However, as will be describedbelow, not only an alternating field, but a steady field, orcombinations of alternating and steady magnetic fields may be employedfor various measurements. If an alternating magnetic field is to beproduced, the field supply may comprise an oscillator and poweramplifier, as described above and if a steady magnetic field, a suitablesource of direct current, for example, a battery, may be used. A steadymagnetic field may also be produced by the use of a permanent magnet. Amagnetic field containing both alternating and steady components may beproduced, for example, by supplying field coils 10 and 11 with bothalternating and direct currents, simultaneously or sequentially, or witha varying direct current. An arrangement with a steady magnetic field isshown in FIG. 33 where the field coils are shown replaced by a permanentmagnet, whose poles are 120 and 121, flanking the pick-up 12, which iselectrically connected to the indicator 14.

When a steady magnetic field is employed, there will be induced withinthe pick-up 12 a voltage proportional to the rate of change of thenumber of lines of force of the field enclosed. With a uniform field,the induced voltage will be proportional to the rate of change ofcrosssectional area of the member, and thus rates of change ofcross-sectional area may be indicated directly. Correspondingly, ratesof change of cross-sectional area may be integrated with respect to thelength of the member, for measurement of rates of change of volume. Andby employing suitable circuits the induced voltages may be integrated,so that indications may be obtained proportionalto the total changes ofthese quantities. The use of steady fields thus provides an alternatemethod of measurement. Also, these methods may be used in combination,by the use of magnetic fields with both alternating and steadycomponents. By suitably employing the voltages developed in this manner,areas and volumes, their changes, and their rates of change may bedetermined most conveniently.

Electromagnetic induction may also be employed to effectuate themeasurement of other quantities which may cause or may be made to causea change in the number of lines of force of a magnetic field enclosed bya pick-up conductor. For example, a displacement may be measured byrelating to it a change in the area or projected area of a pick-up in analternating magnetic field. In corresponding manner, using steady andalternating fields, this method may be employed for measuring position,displacement, velocity, and related quantities, and for producing outputvoltages which are various functions of these quantities.

A general procedure which may be followed is to cause the projected areaof a pick-up in the magnetic field to be varied according to thequantity being measured. (As used herein, projected area means theprojection of the area of the pick-up upon a plane perpendicular to thedirections of the magnetic field passing through the pick-up). Themagnetic field may be alternating, steady, or combinations ofalternating and steady, according to the indication desired. In theabove example, to measure displacement, an alternating magnetic fieldmay conveniently be employed, while a steady magnetic field may beemployed to measure velocity.

FIG. 34 illustrates a field structure and pick-up whose area in themagnetic field is varied according to a displacement, thereby providingmeans for measuring such displacements. The electromagnet 12 6 producesa magnetic field between pole pieces 130 and 131, whose nature dependson the current through the field coil 127, connected to a field supplythrough leads 128. The area inclosed by the pick-up 132 varies accordingto the magnitude and direction of the displacement 138, thus changingthe number of lines of force inclosed by the pick-up.

With reference to voltages induced in the pick-up of FIG. 34, as well asin those described below, when an alternating magnetic field is employedthe induced voltage will be proportional to the number of lines of forceenclosed. Hence changes in cross sectional area, caused bydisplacements, will result in changes in the induced voltage. And if thechange in the number of lines of force enclosed is proportional to thedisplacement, the change in the induced voltage will likewise beproportional to the displacement. By designing the pole pieces 130, 131so that the change in number of lines of force enclosed is a desiredfunction of the displacement, the resulting voltage will be the samefunction of the displacement, thereby providing adisplacement-to-voltage transducer with a predetermined transferfunction. When a steady magnetic field is employed the induced voltagewill be proportional to the rate of change of lines of force enclosed.And again, if the change in the number of lines of force enclosed isproportional to the displacement, the induced voltage will beproportional to the velocity of the displacement.

Illustrative of some of the types of pick-ups which may be employed arethe constructions shown in FIGS. 35 through 46, in which heavy linesrepresent rigid and light lines non-rigid conductors. In FIGS. 35through 43, the direction of the magnetic field is at an angle to theplane of the paper, preferably at a right angle. These figures showpick-ups consisting of single strands of conductor. Alternatively theymay consist of many strands, forming coils for increased output.

The areas of the pick-ups may be made variable by employing numerousconstructions. These include structures employing conductors formed intoyieldable configurations, such as coil springs (FIGS. 35 and 36) andflexible shapes (FIGS. 37 and 38), the use of conductors which areinherently extensible and flexible (FIG. 39), and the use of other formssuch as jointed structures (FIG. 40), and structures employing slidingcontacts (FIG. 41).

FIG. 35 is another view of pick-up 132 of FIG. 34 wherein rigidconductors 134 and 135 are joined by coil springs 136 and 137, and leads133 are connected electrically to an indicator, such as indicator 14 ofFIG. 1. Input displacement 138, applied to conductor 135, causes achange in the number of lines of force of the field enclosed.

FIG. 36 is a modification of FIG. 35 wherein 134a is a rigid conductor,while coil springs 136a and 137a are joined together, to whose juncturedisplacement 138 is applied.

In FIG. 37, 1341; and 1351) are rigid conductors joined by flexibleconductors 139 and 140. Displacement 138 is applied to conductor 1351).

In FIG. 38 the pick-up is formed entirely of flexible conductor 141,which may be of any suitable shape, with displacement 138 appliedthereto.

In FIG. 39 the displacement is applied to flexible, extensible conductor-144 joined to rigid conductors 142. and .143, which in turn are joinedto conductor 1340.

FIG. 40 illustrates a jointed structure comprising rigid conductors withjoints 146, to one of which joints input displacement 138 is applied.

FIG. 41 illustrates the use of sliding contacts; rigid conductor 1-47,to which displacement 138 is applied, makes sliding contact with rigidconductors 142d and 143d which are joined to conductor 134d. Rollingcontacts and contacts with liquid conductors may be similarly employed.

As indicated above, when using alternating magnetic fields, it is oftenconvenient to balance out the voltage induced in an undeflected pick-up.FIG. 42 shows a means of accomplishing this, by suitably shaping thepick-up, applied in particular to the pick-up of FIG. 39. To the voltageinduced in loop 148, the pick-up loop, is added to the voltage inducedin loop 149, which is connected so as to oppose that in loop 148. Thus,if an equal number of lines of force is enclosed by each, the net outputvoltage is zero. The voltage induced within loop 149 may be brought toequality with that of loop 148 by adjusting its area, for example. Inthis manner an indication of zero may correspond with a displace ment ofzero. Balancing loop 149 need not be mounted alongside pick-up loop 148,but may be located in other positions, for example, in front or behindloop 148.

FIG. 43 shows a construction in which an increase in cross-sectionalarea of pick-up loop 150 is accompanied by a decrease in that of pick-uploop 151 when conductor 144a is deflected downward by input displacement138. The output of the loops is intended for connection to aconventional differential amplifier by triple conductor leads 133a, sothat here also, for initially equal areas 150 and 151, an indication ofzero is obtained.

FIG. 44 shows a modified application of the pick-up of FIG. 39 in whichthe conductor 14412 is deflected preferably at right angles to the planeof the undeformed pick-up loop by input displacement 138, and themagnetic field is applied generally parallel to the plane of the pickuploop, and at a right angle to the conductor 1441?. Thus the undeflectedpick-up encloses no lines of force and so produces an indication ofzero. Since the displacement is at an angle to the plane of theundeflected pick-up, a change in the displacement causes a change in theprojected area of the pick-up in the field, and hence in the number oflines of force of the field enclosed by the pickup. However, theconstruction of FIG. 44 is sensitive to the induction of spuriousvoltages by stray fields which make an angle with the plane of thepick-up loop. These may be cancelled in a number of ways, including theuse of balancing loops connected as shown in FIG. 45 or connected asshown in FIG. 42.

FIG. 46 shows an additional pick-up form, in which the magnetic fieldmay be applied as in FIGS. 44 and 45, but in which conductors 154 and156 may undergo deflection when conductor 155 is displaced. Pick-ups ofthe forms of FIGS. 35, 36, 37, and 38 may be similarly operated. Variousbalancing arrangements may likewise be employed with these types ofpick-ups.

FIG. 47 shows a pick-up structure adapted for convenient attachment to asurface undergoing changes in dimensions, such as that produced bystresses. FIG. 48 is an end view of FIG. 47. The pick-up conductor 157,which is shown embedded within a yieldable material, may also befastened to the surface of such material, which may be elastomeric, andwhich is preferably non-conductive. A pick-up conductor or a pick-upstructure may be attached to the member being measured by variousmethods, including cementing, using pressure-sensitive materials andembedding within. The shape of the area outlined by pickup 157 isdetermined by the requirements of the measurement in conventionalmanner.

In general, if a uniform alternating magnetic field is employed, theinduced voltage in a pick-up will be proportional to the area of thepick-up, and if a uniform steady magnetic field, to its rate of changeof areas. Hence, a desired relation between the output voltage and thequantity being measured may be obtained by designing a pick-up so thatits area or rate of change of area are properly related to the quantitybeing measured and employing respectively a uniform alternating orsteady magnetic field.

correspondingly, non-uniform magnetic fields may be employed. In anyalternating magnetic field, regardless of uniformity, the output voltageof a pick-up is proportional to the number of lines of force enclosed,and in any steady field, to the rate of change of lines of forceenclosed. Hence the output voltage depends on both the fielddistribution and the relation of the area of the pick-up to the quantitybeing measured, so that suitable combinations of field distribution andpick-up design may be employed to establish desired relations betweenthe output voltages and the input quantities. The required fielddistributions may be obtained by conventional methods, including propershaping of pole pieces, as for example pole pieces and 161 of FIG. 49,which may be used with the magnetic structure and pickup of FIG. 34.

Forces and related quantites may be measured by employing elasticelements or similar means in conjunction with the above systems.Conductors having suitable elastic properties may be employed directly,for example, in the form of coil springs, for illustration in the mannershown in FIG. 34. One elastic conductor material which may be used forthis purpose is beryllium copper. The configuration of the pick-up ischosen to meet the requirements of the application.

The forces and related quantites need not be applied at one point of theconductor only, but may be distributed along its length. One applicationis to a fiowmeter, in which a taut or elastically suspended conductor isacted upon by a fluid, one construction of which is shown in FIG. 50.Lines of force are produced between the pole pieces 1301; and 1311) ofthe electromagnet 126b, the steady or alternating nature of the magneticfield being determined by the field supply connected to field coil 127bby leads 12%. The lines of force are generally parallel to the plane ofthe area enclosed by pick-up 162 and rigid conductor 163, and at a rightangle to pick-up, 162, which is connected to an indicator by leads 133.Pick-up conductor 162 need not be a straight length of wire, but may beof various other forms for reasons including increased sensitivity, etc.Examples of such forms are the use of a conductor in the form of a flatstrip, or in the shape of a coil spring. The pick-up is contained in atube 164, preferably non-conductive, through which passes the fluidwhose flow is to be measured. As the flow of fiuid increases, its dragincreasingly deflects pick-up conductor 162, increasing the projectedarea of the pickup, and hence the number of lines of force of the fieldenclosed. Thus the output voltage is representative of the fluid flow.

Another application is to a pressure-measuring device, in which adiaphragm, which is deflected by the pressure being measured, serves asthe movable portion of a pickup, one form of which is shown in FIGS. 51and 52. In another example, a pick-up conductor may be secured to thediaphragm, one form of which, is shown in FIGS. 53 and 54. In FIG. 51the lines of force of the magnetic field, produced in any known manner,for example, in the manner shown in FIG. 50, are assumed parallel to theplane of the paper, and horizontal. FIG. 52 is a center section view ofFIG. 51. The pick-up consists of conducting diaphragm 164, which may becorrugated if desired, held to body 165 by clamping ring 166. Contact ismade to the top and bottom of diaphragm 164, connection being made toleads 133, with the aid of rigid conductor 167. Both clamping ring 166and body 165 are preferably nonconducting. The inlet 168 is connected tothe pressure to be gauged. A change in pressure causes diaphragm 164 tobow in or out, causing a variation in the number of lines of forceenclosed within the pick-up loop according to the magnitude anddirection of the pressure change.

FIGS. 53 and 54 illustrate a similar device in which diaphragm 164a,which is preferably a non-conductor, is clamped to body 165 by clampingring 166, yieldable pick-up 169 being fastened to diaphragm 164a.Alternatively, pick-up 169 may be molded Within diaphragm 164a. Theelectrical circuit is completed through rigid conductor 167 andconnected to an indicator by leads 133. FIG. 54 is a center section viewof FIG. 53. Operation is as described above for FIGS. 51 and 52. InFIGS. 51, 52,

19 53, and 54, the bodies are shown to be round, but any suitable shapemay be used for this purpose.

Electromagnetic induction may also be employed for the measurements ofirregular areas such as those defined by boundary lines, for example,maps, charts and mathematical curves such as that shown in FIG. 55. Thearea is outlined on sheet 171, preferably non-conductive, by anyconductor, which may be a line of conductive material, such as aconductive pencil, ink, metals in solution or suspension, elastomericmaterial, or a fine wire, which may be mounted on sheet 171, and isprovided with leads 133 which are connected to an indicator, such as 14of FIG. 1. The outlined area is placed within a uniform alternatingmagnetic field, in the general manner of the pick-up conductor 12 ofFIG. 1, or the pick-up conductor 132 of FIG. 34, the lines of force thuspreferably making a right angle with th plane of said area.

In operativcly employing the arrangement of FIG. 55, it is apparent thata voltage will be induced within the conductor 170, the voltage beingproportional to the area outlined by conductor 170. The indicator,electrically connected to leads 133, can be calibrated directly toindicate areas in the manner above described.

In order to accomplish these objectives, there are various forms andmanners of establishing electrical contact with the pick-ups inaccordance with out invention. For example, in FIG. 56, leads 133 areattached to a strip of non-conductive material or tape 172, which may betransparent, it being applied to curve 170 to establish contact to thecurve, for example at conductor 173. FIG. 57 is an enlarged view ofcontact-making device 172, showing leads 133 terminating in a pair ofrelatively short, closelyspaced parallel narrow strips or leads ofconductive ma terial 175 and 176, between which a barrier or removablemask may be placed to preclude possibility of a short circuit. Thematerial 175, 176, may be coated on one side with a pressure sensitiveadhesive to conveniently hold it to a surface containing a curve; orother means of attachment may be used. The material may be treated onthe edges and the other side with such material as to allow a desirableconductive solid or liquid to adhere to the material. In use, the coatedmaterial is placed over conductor 173 of curve 170 in such manner thatthe parallel strips 175 and 176 intersect conductor 173. The outline ofthe portion of said area covered by the material may then be marked witha suitable solid or liquid conductor, connecting the strips along thetreated surface and edges 177 of the material, following the outline ofconductor 173, until contact is made with the curve, which isfacilitated by the use of transparent material. The curve is preferablyinterrupted under material 172 so that the output voltage will not beshunted. In this manner an electrically conductive circuit isestablished from one of the parallel strips, around the perimeter of thearea to be measured, and back to the other parallel strip. If a uniformalternating magnetic field is employed, a voltage will be inducedproportional to the area enclosed.

Many variations of the above-described contact-making device may beconstructed. As an example, the material, which may be transparent asset forth, may be made large enough so that the entire outline may betraced in conductive solid or liquid on the material.

If it is desired to perform mathematical operations on curves, inaddition to measuring their areas, a number of procedures may befollowed. For example, the sheet on which the area is outlined may bedeformed in various ways a yieldable material and conductor being used,to represent certain operations. Alternatively, the curves may beoutlined on suitable surfaces which do not lie in a plane.

Additional methods of performing mathematical operations on curvesinclude the use of non-uniform fields, having field distributionsaccording to the operations to be performed. For example, the outlinedarea may be positioned within a non-uniform alternating magnetic field,such as that which may be produced by a field structure such as that ofFIG. 49, in the general manner of pick-up 132 of FIG. 49. In thismanner, various computations may be rapidly and conveniently performed.

It should be understood that in any of the applications ofelectromagnetic induction for the making of various measurements, thepick-ups may be acted upon by various types of fields and combinationsof fields. These may be steady or alternating ,and they may differ invarious ways, including amplitude, direction, distribution, and in beingapplied simultaneously, separately, or cyclically, and if alternating,in frequency and phase. Likewise, a single field system may act onseveral pick-ups or on a portion or portions of pick-ups.

When steady fields are being used, an auxiliary coil such as coil 60 ofFIG. 20, may also be used, and also connected as a balancing coil, forexample as shown in FIG. 21, to compensate for induced voltagesresulting from rotation, as well as to cancel spurious voltages inducedby variation in the steady field or by stray fields.

In employing our system for plethysmographic purposes, as aboveindicated, the conventional venous occlusion method is used, permittingmeasurements of the total blood flow. This can be accomplished in themanner described in the previously filed application Ser. No. 66,523,now Pat. No. 2,649,573. The same method renders our invention adaptablefor the general measurement of fluid flow where elastic non-conductingtubes can be employed as a conduit for a fluid by storing the effluentand measuring, by the method above described, the rate of increase ofvolume, which equals the rate of flow.

Thus our invention has utilized the properties of electromagneticinduction in the electrical measurement of areas and their rates ofchange and in the transducing of physical quantities (such asdisplacement, flow, force or pressure) into electrical signals bycausing such quantities to provide corresponding changes in area.

The term conductor arrangement as used herein means either a conductorper se in a configuration adapted to provide the functions andadvantages described, or a conductor mounted on a support, where theircombination provides such functions and advantages.

In the above description, the invention has been disclosed merely by wayof example and in preferred manner; but obviously many variations andmodifications may be made therein. It is to be understood, therefore,that the invention is not limited to any specific form or manner ofpracticing same, except insofar as such limitations are specified in theappended claims.

What is claimed is:

1. In an electrical system for performing a measurement upon any one ofa wide variety of shapes having differing magnitudes of area ordiffering contours or both, an electrical pickup device comprising apickup conductor arrangement having a conductor, and a pair of conductorleads connected respectively to the ends of said conductor forconnecting said ends to measuring apparatus, said conductor being ofthin, soft, flexible, essentially non resilient, conductive materialthroughout its length, said conductor arrangement including means forcausing said conductive material to maintain a close juxtaposition toand a configuration essentially flatly conforming to the contour of atleast part of the periphery of any selected one of said shapes, saidmeans including means for adjusting the length of the portion of saidconductor arrangement along said contour to conform to said contour, thetransverse dimension of said conductor in a direction normal to saidcontour being of a substantially smaller order of magnitude than theminimum transverse dimension of any of said shapes.

2. In an electrical measuring system for performing a measurement uponany selected one of a Wide variety of essentially plane shapes to bemeasured having differing magnitudes of area or differing contours orboth, in combination a pickup conductor arrangement having a conductor,and a pair of conductor leads connected respectively to the ends of saidconductor for connecting said ends to measuring apparatus, saidconductor being of a thin, soft, flexible, essentially non-resilient,conductive material throughout its length, said conductor arrangementincluding means for causing said material to maintain a closejuxtaposition to and a configuration essentially flatly conforming tothe contour of at least part of the periphery of any selected one ofsaid shapes, said last means including means for adjusting the length ofthe portion of said conductor arrangement along said contour to conformto said contour, the transverse dimension of said conductor measured inthe plane of any of said shapes being of a substantially smaller orderof magnitude than the minimum transverse dimension of any of saidshapes.

3. In an electrical system for performing a measurement upon a widevariety of shapes having perimeters of differing areas or difieringcontours or both, an electrical pickup device comprising a pickupconductor arrangement having a conductor, and a pair of conductor leadsconnected respectively to the ends of said conductor for connecting saidends to measuring apparatus, said conductor being of a thin, soft,flexible, essentially nonresilient, conductive material throughout itslength, said conductor having a configuration readily conformable to anyof said contours and permitting said material to maintain a closejuxtaposition to and a configuration essentially conforming to thecontour of at least part of the periphery of any selected one of saidshapes, and said arrangement being extensible essentially withoutresistive force to accommodate different perimeter lengths of saidshapes, the transverse dimension of said conductor measured in adirection normal to said periphery being of a substantially smallerorder of magnitude than the minimum transverse dimension of any of saidshapes.

4. In an electrical system for performing a measurement upon a widevariety of essentially plane shapes having perimeters enclosingdiffering areas or of differing contours or both, an electrical pickupdevice comprising a pickup conductor arrangement having a conductor of alength greater than the longest periphery of all of said shapes to bemeasured, and a pair of conductor leads con nected respectively to theends of said conductor for connecting said ends to measuring apparatus,said conductor being of a thin, soft, flexible, essentiallynon-resilient, conductive material throughout its length, said conductorhav ing a wavy configuration disposed in a geometric surface and readilyconformable to any of said contours and permitting said material tomaintain a close juxtaposition to and a configuration essentially flatlyconforming to the contour of the entire periphery of any selected one ofsaid shapes, and said arrangement being extensible essentially withoutresistive force to accommodate diiferent perimeter lengths of saidshapes, and geometric surfaces of said wavy configuration beingsubstantially perpendicular to the plane of said selected one shape, thetransverse dimension of said conductor arrangement measured in a planeof any of said shapes being of a substantially smaller order ofmagnitude than the minimum transverse dimension of any of said shapes.

5. An electrical pickup device as in claim 3 wherein said shapes are thecross-sections of members to be measured, and said pickup conductorarrangement is in the form of a plurality of spaced coils with equippedcentral openings, each coil having at least a portion comformable tosaid contour, and said coil portions being independently adjustable inlength to conform to the contour of any selected one of said shapes.

6. An electrical pickup device according to claim 5, each of said coilshaving undulating portions lying generally parallel to the surface ofsaid selected member.

7. An electrical pickup device as in claim 3 wherein said shapes are thecross-sections of members to be measured and said pickup conductorarrangement is in the form of a plurality of coils with aligned centralopenings proportioned for operatively accommodating therein the memberbeing measured, each of said coils being peripherally extendible, andconnected in series with one another and with said leads.

8. An electrical pickup device as in claim 3 for use in the volumemeasurement of a member having various cross-sections constituting saidshapes, wherein said pickup arrangement is in the form of a plurality ofcoils in substantially parallel planes, with means extendingsubstantially perpendicularly of said coils for interconnecting saidcoils, and said conductor leads being connected to said coils.

9. An electrical pickup device as in claim 3 for use in thecross-sectional area measurement of a member, comprising an expandablelength of non-conducting tape, said conductor being supported by saidtape.

10. An electrical pickup device as in claim 3 for use in thecross-sectional area measurement of a member, comprising an expandablelength of non-conducting tape, said conductor being secured to a surfaceof said tape.

11. An electrical pickup device as in claim 3 for use in thecross-sectional area measurement of a member, comprising an expandablelength of non-conducting tape, said conductor being disposed within thebody of said tape intermediate the opposite surfaces thereof.

12. An electrical pickup device as in claim 5 for use in thecross-sectional area measurement of a member, wherein said coils are insubstantially parallel planes with aligned central openings proportionedfor operatively accommodating therein said member, each of said coilsbeing expandable, said coils being electrically connected to each otherin parallel, and two conductor leads connected to said plurality ofparallel coils.

13. An electrical pickup device as in claim 3 for use in thecross-sectional area measurement of a member, wherein said conductorarrangement comprises a helical coil with a central opening foroperatively accommodating the member, the coil being expandable and madeat least in part of said conductor.

14. An electrical pickup device as in claim 3 for use in thecross-sectional area measurement of a member, comprising a helicallywound expandable non-conducting tape, said conductor being supported bysaid tape, whereby said conductor forms a helical coil with a centralopening, the proportions of said tape and coil being such that saidcentral opening will operatively accommodate said member, said conductorcontaining undulating portions, whereby the conductor will expand uponthe operative expansion of the tape.

15. An electrical pickup device for use in the crosssectional areameasurement of a member according to claim 9, said conductor being ofgeneral zig-zag configuration.

16. An electrical pickup device as in claim 3 for use in the crosssectional area measurement of a member, comprising a pickup device as inclaim 3 comprising a coil of conductive material, at least one portionof said coil being deformable and proportioned for embracing engagementwith the member, a coil system comprising at least one auxiliary rigidcoil, means for effectively positioning said coil system to cause itsprojection in any direction to remain proportional to that of theundeformed pickup coil, and conductor leads operatively connected toeach of said coils.

17. An electrical pickup device according to claim 1, said means furtherincluding means for exerting a force against said pickup atsubstantially right angles thereto.

18. In an electrical system for use in a measurement dependent upon thecross-sectional area of a member, a yieldable open-ended tubeproportioned for embracing engagement with the said member, said tubehaving thereon peripherally expandable electrical conducting pickupmeans circumferentially disposed about said tube, the terminal portionsof said coil being in contiguous relation to and in insulated contactwith one another at a point substantially on the perimeter of said area,and conductor leads connected to said terminal portions.

19. In an electrical system for use in an electrical measurementdependent upon the cross-sectional area of a member, an. electricalpickup device comprising a yieldable band proportioned for embracingengagement with the member, a peripherally expandable pickup coilcircumferentially disposed about the band, the terminal portions of saidcoil being in contiguous relation to and in insulated contact with oneanother at a point substantially on the perimeter of said area, andconductor leads connected to said pickup coil.

20. In an electrical system for use in an electrical meas urementdependent upon the cross-sectional area of a member, an electricalpickup device comprising a yieldable band proportioned for embracingengagement with the member, a peripherally expandable pickup coildisposed along the inner surface of the band, the terminal portions ofsaid coil being in contiguous relation to and in insulated contact withone another at a point substantially on the perimeter of said area, andconductor leads connected to said pickup coil.

21. An electrical pickup device as in claim 3 for use in thecross-sectional area measurement of a member, comprising an inflatablecufl? proportioned for embracing engagement with the member, and whereinsa d conduc: tor arrangement comprises an expandable pickup coildisposed along the inner surface of the cuff, and sa1d conductor leadsare connected to said pickup coil.

22. An electrical pickup device as in claim 3 for use in thecross-sectional area measurement of a member, comprising an annularchamber having an inner wall of pliable material proportioned forembraclug engagement with the member, an air conduit in communicationwith said chamber, said conductor arrangement comprising an expandablepickup coil along the outer surface of sa1d inner wall, and saidconductor leads being connected to said pickup coil.

23. An electrical pickup device for use in the crosssectional areameasurement of a member according to claim 22, said chamber having arigid outer cylindrical wall, and said inner wall being of elasticmaterial and being attached to the lateral peripheral edges of saidrigid wall.

24. An electrical pickup device as in claim 3 for use in thecross-sectional areas measurement of a member, comprising a yieldablecuff proportioned for embracing engagement with the member, saidconductor arrangement comprising an expandable pickup coilcircuferentially disposed about and secured to the cuff and an auxiliarynon-expandable conducting coil secured to said cuff, and conductor leadsoperatively connected to said pickup and auxiliary coils.

25. An electrical pickup device as in claim 3 for use in thecross-sectional area measurement of a member, comprising a yieldableopen-ended tube made of a plurality of inter-engaged strands, said tubebeing proportioned for embracing engagement with said member, said tubehaving circumferentially disposed strands of conducting materialconstituting said conductor arrangement.

26. An electrical pickup device as in claim 3 for use in thecross-sectional area measurement of a member, com prising a yieldableopen-ended tube made of a plurality of courses of inter-engaged strandsof conducting material constituting said conductive arrangement, saidtube being proportioned for embracing engagement with said member, andtwo said conductor leads being connected to respective courses atlaterally opposite edges of said tube.

27. An electrical pickup device as in claim 3 for use in thecross-sectional area measurement of a member, comprising a yieldableopen-ended tube made of a plurality of courses of inter-engaged strands,certain of said courses having strands of conducting material andcertain others of said courses having strands of non-conductin 24material, said conducting strands constituting said conductivearrangement, said tube being proportioned for embracing engagement withsaid member, and two said conductor leads being connected to laterallyopposite courses made of strands of conducting material.

28. An electrical pick-up device for use in the crosssectional areameasurement of a member according to claim 27, said courses withconducting and nononducting strands being alternately arranged.

29. An electrical pick-up device for use in the crosssectional areameasurement of a member according to claim 25, the said inter-engagedstrands being of knitted construction with loops arranged in parallelcourses and intersecting Wales.

30. An electrical pick-up device for use in the crosssectional areameasurement of a member according to claim 25, the said inter-engagedstrands being of woven construction.

31. An electrical pickup device as in claim 3 for use in thecross-sectional area measurement of a member, said conductor arrangementcomprising a flexible expandable pickup conductor, and a substantiallyrigid con ductor bridging the opposite end portions of said pickupconductor, and said conductor leads being connected respectively to bothof said conductors.

32. An electrical pickup device as in claim 3 for use in thecross-sectional area measurement of a member, said conductor arrangementcomprising a flexible expandable pickup conductor having undulatingportions thereon, and a substantially rigid conductor of archedconstruction bridging the opposite end portions of said pickup conductorand in the same plane as said pickup conductor, and said conductor leadsbeing connected respectively to said pickup and rigid conductors.

33. An electrical pickup device as in claim 3 for use in the volumemeasurement of a member, said conductor arrangement comprising aplurality of coils in substantially parallel planes, said coils beingmade of conducting material, at least one of said coils being flexibleand adjusting, and at least another being a substantially rigid coil.one end of at least one of said rigid coils being connected to thecorresponding end of at least one of said flexible, coils, and saidconductor leads being connected respectively to the other ends of saidpickup and rigid coils.

34. An electrical pickup device as in claim 3 for use in the internalcross-sectional area measurement of a member, comprising an expandablestructure proportioned for engagement with the member, and saidconductor arrangement comprising an expandable pickup coil disposedalong the surface of said structure, said conductor leads beingconnected to said pickup coil.

35. An electrical pickup device as in claim 3 for use in the internalcross-sectional area measurement of a member, comprising an inflatablechamber proportioned for engagement with the member, said conductorarrangement comprising an expandable pickup coil disposed along asurface of the chamber, and said conductor leads being connected to saidpickup coil.

36. An electrical pickup device as in claim 3 for use in the internalcross-sectional area measurement of a member, comprising a tubularchamber having a wall of pliable material proportioned for engagementwith the member, an air conduit in communication with said chamber, saidconductor arrangement comprising an expand- 1 able pickup conductoralong a surface of the chamber, and said conductor leads being connectedto said pickup coil.

37. In an electrical system for performing an electrical measurement, anelectrical pickup device adapted to be formed into a variety of shapeshaving perimeters of differing areas or contours or both, comprising acoil of conductive material having at least one loop of conductor, saidcoil being deformable in at least one portion thereof to create suchdiffering shapes, the terminal portions of said coil being in contiguousrelation to and in insulated contact with one another at a pointsubstantially

